Effect of vitamin D supplementation on circulating fibroblast growth factor-23 concentration in adults with prediabetes.

Background: Recent meta-analyses report that vitamin D supplementation increases blood fibroblast growth factor-23 (FGF23) level.
Objectives: To determine the effect of 4000 IU/day of vitamin D ₃ for 12 months on circulating FGF23 levels. We also examined the association of the achieved 25-hydroxyvitamin D level [25(OH)D] with the FGF23 level at 12 months and with 12-month changes in FGF23.
Methods: An ancillary analysis among adults 70 years and older with prediabetes who participated in a trial comparing vitamin D ₃ 4000 IU/day with placebo. Plasma intact FGF23 and serum 25(OH)D were measured at baseline and month 12 (M12).
Results: Characteristics of the 52 participants (vitamin D ₃ n = 28; placebo n = 24) did not differ significantly aside from more women than men in the vitamin D ₃ group. Mean ± SD age was 73.8 ± 3.7 years, BMI 31.3 ± 4.2 kg/m2, and glomerular filtration rate (GFR) 76.3 ± 11.8 mL/min/1.73m ² Baseline serum 25(OH)D level was 33.4 ± 10.8 ng/mL and increased at M12 to 54.9 ± 14.8 ng/mL in the vitamin D ₃ group versus 33.4 ± 14.9 in the placebo (p < 0.001). At baseline, GFR was inversely associated with FGF23 (r = - 0.349, p = 0.011). Change in FGF23 level at M12 did not differ significantly between vitamin D ₃ and placebo. In all participants combined, the achieved serum 25(OH)D level at M12 was not significantly associated with the M12 plasma FGF23 or the M12 change in FGF23.
Conclusion: In obese older adults with sufficient vitamin D status and normal renal function, vitamin D ₃ 4000 IU/day for 12 months did not significantly alter plasma intact FGF23 levels.
Clinicaltrials: gov NCT 01,942,694, registered 9/16/2013.
(© 2023. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)